The invention relates to a cutting knife for a cutting tool for severing a cement bead of a window pane cemented in a motor vehicle. The cutting knife is formed from a flat material which is bent into the shape of an U. The knife comprises a cutting portion forming one leg of the U, a securement portion forming another leg of the U, and an intermediate bridge that connects the cutting portion with the securement portion. The securement portion comprises an opening at its free end for securing the knife to an oscillatory drive unit of the cutting tool and tapers from this securement opening toward the intermediate bridge.
U-shaped cutting knives are known for example from DE-U1 86 17 670 or EP-B1 0 141 035. Such knives are known especially for removing windshields from motor vehicles when necessary due to window damage or leakage. If the problem is only leakage, one must take care that the window pane is not damaged by the high frequency oscillation of the cutting knife. In addition, when cutting through the cement bead that cements the window pane to the vehicle body flange, care must be taken not to damage the painting of this body flange. Otherwise, such damage could later lead to corrosion. Finally, the particular geometry of the window must be observed when removing the window, which depends upon the type of automobile and how the window is assembled.
With the conventional cutting knives of the art it has been found that considerable skill is still necessary to cut through the cement bead. Considerable force must be applied. In addition, the danger of the worker breaking the window with the oscillatory knife is still high.
It is an object of the present invention to provide an improved cutting knife which allows an easy removal of windows from motor vehicles.
It is a further object of the invention to provide an improved cutting knife which avoids clamping of the knife within the cement bead and requires less force than prior art knifes.
These and other objects of the invention are solved by providing a cutting knife of the above-mentioned type, wherein the securement portion comprises a curved section at the end thereof, said end being adjacent the intermediate bridge. The position of the cutting portion with respect to the cement bead when removing the windshield is optimised by the curved section. As a result, the cement bead can be cut with considerably less force. Further, a clamping of the knife in the cement bead is avoided.
In a preferred embodiment of the present invention, the curved section comprises a convex side edge facing the cutting portion, and a concave side edge opposing the cutting portion. Preferably, the curvature curvature of the the convex side edge is smaller than the curvature of the concave side edge.
With this feature, the geometry of the cutting portion with respect to the securement portion is further improved and the guidance of the cutting knife, preferably having a crescent-shaped curvature, when drawn through the cement bead, is improved. Furthermore, the stroke of the oscillation is better utilised when actually cutting through the cement bead.
In a further embodiment of the present invention, at least a side of the cutting portion that faces the securement opening comprises a serrated or saw-like cutting edge. This makes cutting through the cement bead easier, especially if it is a tough material, for example polyurethane.
In a further embodiment of the invention, a side of the cutting portion that opposes the securement opening comprises a cutting edge with a peak angle of at least 30xc2x0. Providing a cutting edge also on the side opposed to the securement opening simplifies the return of the cutting portion through a section which has already been cut, should this be required. Since the cutting edge on the side opposed to the securement opening has a large peak angle, i.e. is relatively xe2x80x9cdullxe2x80x9d, the cross-section of the cutting portion is only slightly reduced, which on the whole adds to stability and reduces the danger of breakage.
In an alternative embodiment, a side of said cutting portion that opposes said securement opening comprises a blunt edge. This has the advantage that the cross-section of the cutting portion is further enlarged and thus the possibility of breakage further reduced.
In another aspect of the present invention the cutting portion comprises a cross-section with a central section defined by two parallel surfaces, which join into a sharp angle cutting edge at least on an end of the cutting portion facing the securement opening. This guarantees an optimal cutting process. In particular, the enlarged cross-section of the cutting portion leads to a greatly reduced danger of breakage. In addition, a possible clamping of the cutting knife in the cement bead is counteracted.
According to another aspect of the present invention, the cutting portion comprises a central section having parallel surfaces, said central section having one end adjoining said cutting edge, and further having another end adjoining a crowned or conical section. A distinctly improved cutting operation is achieved and the danger of breakage is also reduced. In addition, the cutting portion can be provided with a serrated or saw-like cutting edge in these embodiments, at least on the side facing the securement opening.
It will be understood that these embodiments of the invention can also be combined with a curved portion as described above on the securement portion and that the serrated edge can be provided on both sides of the cutting portion.
Further, it will be understood that the above-mentioned features and those to be discussed below may be used not only in the above combinations, but taken alone or in other combinations without departing from the scope of the present invention.